In the production of music and sound, musicians and sound engineers create audio compositions that include sequences of multiple channels of audio data. To create such compositions, musicians and sound engineers need to adjust levels and apply other effects to multiple channels of audio data. Musicians and sound engineers typically use a digital audio workstation for these tasks.
A digital audio workstation typically includes a host computer that may include peripherals for audio processing. Software on the host computer keeps track of both data files that store the multiple channels of audio data and the various parameters used to combine them into a composition. The software also performs audio processing functions and provides a graphical user interface to assist the musician or sound engineer to manipulate the composition.
A digital audio workstation also sometimes includes a control surface that provides a tactile user interface through which the musician or sound engineer manipulates the composition. Such control surfaces often include numerous mechanical control devices including, but not limited to, rotary encoders, potentiometers, faders, loop controllers, joysticks, touchpads, and switches, etc. Such control surfaces often include numerous display devices including, but not limited to, light emitting diode (LED) displays, alphanumeric displays and graphical displays. For example, each rotary encoder may be surrounded by a ring of LEDs that displays the setting defined by the position of the rotary encoder.
Information from the control devices is periodically sent to the host computer for use in editing or playback of the composition. Information from the host computer is periodically sent to the control devices to update the displays. Control surfaces connect to host computers through a number of different mechanisms, including, but not limited to networks, such as Ethernet, and busses, such as a MIDI serial bus and a universal serial bus (USB).
In large control surfaces, there may be a large number of control devices and display devices. Thus, a significant amount of bandwidth is used to exchange information between the host computer and the control surface.
For example, the Pro Control control surface from Digidesign (a division of Avid Technology, Inc.) connects to the Pro Tools software from Digidesign through an Ethernet connection. Ethernet protocol packets encapsulate MIDI data representing the control information and display information. In this interface, to ensure reliable packet delivery, packets are check summed and acknowledged. If an acknowledgement is not received in a reasonable period of time, the packet is retransmitted. No other packet is transmitted until an acknowledgement is received. If a packet is retransmitted several times, the connection is presumed to be broken.
With a large number of control and display devices, MIDI formatted messages are inefficient, because they carry only 7-bit data. Also, the use of acknowledgement messages introduces delay and reduces the utilization of the network connection between the host and the control surface.